层流火焰动力学研究 进展及展望 北京大学工学院力学与工程科学系 第一届全国青年燃烧学术会议 2015 年 9 月 日, 上海. Peking University

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1 第一届全国青年燃烧学术会议 2015 年 9 月 日, 上海 层流火焰动力学研究 进展及展望 陈正 北京大学工学院力学与工程科学系 Peking University 邮件 : cz@pku.edu.cn 网站 :

2 内容提要 1. 背景介绍 2. 代表性研究进展 3. 当前研究前沿 4. 总结展望 2

3 内容提要 1. 背景介绍 2. 代表性研究进展 3. 当前研究前沿 4. 总结展望 3

4 研究对象 : 基础燃烧过程 点火 最小点火能 ( 球形传播火焰 ) 点火温度 / 延迟时间 ( 对冲火焰 ) CH 4 /air Q 火焰传播 火焰速度 ( 球形传播火焰 对冲火焰 平面火焰 ) 火焰稳定性 ( 球形传播火焰 平面火焰 热声耦合 ) 火焰驻定 ( 本森灯火焰 钝体稳定火焰 ) 熄火 熄火拉伸率 ( 对冲火焰 球形传播火焰 ) 可燃极限 ( 球形传播火焰 管内传播火焰 ) 4

5 研究内容 研究与替代燃料和先进燃烧技术相关的基础燃烧问题 : 基础燃烧理论研究 替代燃料燃烧特性研究 点火 火焰传播与熄火 近极限 多组元 高压 低温

6 内容提要 1. 背景介绍 2. 代表性研究进展 3. 当前研究前沿 4. 总结展望 6

7 2.1 Flame ball and ignition theory What happens after spark ignition in a premixture? CH 4 /air Flame radius a propagating spherical flame a self-extinguishing flame Q? a stationary flame ball a decaying ignition kernel Time Depending on the mixture property and ignition energy, there are four possible outcomes. 7

8 What is flame ball? T=T f Y F ~1-1/r Zeldovich (1944): Purely diffusion-controlled stationary spherical flames Dynamics dominated by 1/r tail Ya. B. Zel dovich T~1/r Deshaies and Joulin (1984): 0 Burnt products R f Fuel, oxidizer, and products r Adiabatic flame balls are unstable! Ronney (1990): Stationary flame balls Lean H 2 -air mixtures? 1 cm 1.67 sec 4.00 sec 9.00 sec P. D. Ronney

9 Theory on critical ignition conditions What is the controlling length scale for flame initiation? How is it related to the minimum ignition energy? Flame thickness Lewis and Von Elbe (1961) Minimum flame kernel ~ flame thickness. Minimum ignition energy ~ cube of flame thickness. Q? Flame ball radius Deshaies & Joulin (1984), Zeldovich et al. (1985), Champion et al. (1986) Adiabatic flame balls are unstable: collapse or expand. Minimum flame kernel size ~ flame ball radius. Minimum spherical flame radius He (2001), Chen & Ju (2007CTM), Kelley & Law (2008CNF), Chen et al. (2011PCI) Propagating spherical flame with radius less than flame ball radius exists. Flame initiation might not be controlled by flame ball radius. 9

10 2.2 Activation-energy asymptotics (AEA) Fluids: boundary layer theory (Prandtl): Re x >>1 Flame: large activation energy: E a >>1 Math: singular perturbation (matched asymptotics) reaction zone preheat zone equilibrium zone Y F,u T u ω T b δ f δ R Boundary Layer Premixed Flame

11 Reduced chemistry and flame structure N. Peters Premixed flame with four-step chemistry CH 4 +2H+H 2 O=CO+4H 2 CO + H 2 O=CO 2 +H 2 H + H + M=H 2 + M O 2 + 3H 2 =2H+2H 2 O 11

12 内容提要 1. 背景介绍 2. 代表性研究进展 3. 当前研究前沿 4. 总结展望 注 : 由于向一些国外同行咨询了相关建议, 故该部分内容为英文 12

13 3.1 Laminar flame theory Trend: from one-step chemistry to multi-step chemistry Fuel Product Fuel Radical Product Reaction sheet Focus: ignition, extinction hydrodynamics & instability near-flammability limit Review papers: Matalon (2009), Smooke (2013) PCI Sanchez & Williams (2014), Pitz (2014),...PECS 4-step chemistry (N. Peters) CH 4 +2H+H 2 O = CO+4H 2 CO+H 2 O = CO 2 +H 2 H+H+M = H 2 +M O 2 +3H 2 = 2H+2H 2 O Matalon (2007), Candel (2014) Linan (2015) Annual Rev. Fluid 13

14 3.1 Laminar flame theory Two-step chemistry: chain branching reaction F Z 2Z chain termination reaction Z M P M flame front R Radical, Y Z Fuel, Y F Temperature, T Asymptotic analysis: f ( U, R; q, q, Le, Le, h) t r F Z 0 burned zone U unburned zone Effects of radical reaction and transport [1] Flame quenching [2,3] Thermal vs. chemical ignition efficiency [4] [1] H. Zhang, Z. Chen, Combustion and Flame, 158 (2011) [2] H. Zhang, Z. Chen, Combustion Theory and Modelling, 17 (2013) [3] H. Zhang, P. Guo, Z. Chen, Combustion Science and Technology, 185 (2013) [4] H. Zhang, P. Guo, Z. Chen, Proceedings of the Combustion Institute, 34 (2013)

15 3.1 Laminar flame theory Theory on flame propagation in a tube completion & surface reactions Y F T chain-branching reaction at x=0 adiabatic wall, T=T ad Fuel/air wall radical heat 0 T C Y Z non-adiabatic wall x wall u d Two flame quenching mechanisms Thermal quenching (heat loss) Kinetic quenching (radical quenching) Effects of wall quenching of radicals [1] Heat recirculation, radical recirculation? [1] B. Bai, Z. Chen, H. Zhang, S. Chen, Combustion and Flame, 160 (2013)

16 3.2 Flame-chemistry International Workshop on Flame Chemistry, 2012, 2014 Challenges in flame-chemistry: What are the new findings and the major knowledge gaps in understanding ignition and flame chemistry at extreme conditions? How to formulate theoretical and experimental strategies to narrow the knowledge gap and to develop better predictive kinetic models? What are the major differences in chemistry between homogeneous ignition and laminar and turbulent flames? How does low temperature chemistry affect ignition and combustion in high pressure HCCI, PPCI, RCCI, and gas turbine engines? How can we quantify the fidelity of high pressure flame chemistry and transport data? How can we extract constraining information for model construction from macro measure ignition delay, flame speeds, and extinction limits? What diagnostics can we apply to high pressure systems? How does turbulence and chemistry interact in high pressure and Reynolds flows? Can this workshop formulate collaborative relationship in research? 16

17 3.2 Flame-chemistry International Workshop on Flame Chemistry, 2012, 2014 Collaboration: propene (2012), petane (2014) An experimental and modeling study of propene oxidation. Part 1: Speciation measurements in jet-stirred and flow reactors (2014 CNF) Part 2: Ignition delay time and flame speed measurements (2015 CNF) Authors: Battin-Leclerc, Curran, Dryer, Herbinet, Ju, Konnov, Nilsson, Oehlschlaegerc, Petersen, Sung (Burke et al CNF) 17

18 3.3 Ignition minimum ignition energy Background: High-altitude relight High-speed combustion Safety (fire, explosion) Q? Focus: Chemical effect (plasma) Turbulence (flow, transport) Diluents (H 2 O, CO 2, ultra-lean) Spray (vaporization) Solid propellants (B, Al) Review papers: Ju & Sun (2015) PECS Mastorakos (2009) PECS Aggarwal (2014) PECS Dreizin (2015) PECS Ignition of spray flame Han & Chen (2015) Combust. Flame 18

19 3.3 Ignition ignition delay time Background: Data for chemical model development and validation High T: Shock tube Low T: RCM Focus: Inhomogeneous ignition Strong/weak ignition ignition vs. flame Hanson (2014) PECS Review papers & groups: Hanson & Davidson (2014) PECS Sung & Curran (2014) PECS Grogan et al. (2015) CNF Wooldridge Group Ihme Group Mansfield (2014) CNF 19

20 3.3 Ignition Internal Comb. Engine Background: Ignition control HCCI, RCCI Engine knock Focus: Fuel design/reactivity control End-gas autoignition (flame propagates in autoigniting mixture) Pre-ignition & super-knock Detonation development Hot spot Burned gas Subsonic deflagration End gas Pressure wave Flame front (Zhang 2013) ξ u Review papers & research groups: Yao (2009), Lu (2011), Saxena(2013) PECS Drake (2007), Dec (2009), Kalghatgi (2015) PCI Kalghatgi (2014), Wang (2015) IJER Bradley, Wooldridge, Wang, Wei, Chen Supersonic auto-ignition Developing detonation ε ξ l (Bradley et al. 2002) 20

21 3.3 Ignition flame, autoignite/detonation Focus: flame propagates in autoigniting mixture T(K) P(atm) Normal flame Autoignition Detonation Q(J/m 3 s) x (cm) Simulation (Yu and Chen, 2015CNF) Exp. (Qi, Wang 2015CNF) 21

22 Q(J/m 3 s) Multi-stage ignition at low temperature nc 7 H 16 /air 780 K, 40 atm LTI ITI HTI t(ms) For large fuels, multi-stage ignition occurs at low T. Heat release during different ignition stages might produce different pressure pulses. Complicated reaction-pressure wave interactions happen. P. Dai, Z. Chen, Combustion and Flame, (2015) online. T(K) P(atm) Q(J/m 3 s) D D1 D1 6 P 6 S1 D2 S1 S2 (a) 8 S1 S1 D2 x(cm) S1 S D2 7 8 (b) (c)

23 3.4 Flame propagation S u Workshop on Laminar Burning Velocity (2012, 2015 France) Background: Data for chemical model development and validation Input for turbulent premixed flame modeling Focus: Accuracy/uncertainty High pressure/temperature Review papers: Egolfopoulos et al. (2014) PECS Ranzi et al. (2012) PECS Laminar flame speed, Su (cm/s) Egolfopoulos et al. (2014) PECS 40 CH4+Air Exp. Mechanism A Mechanism B Equivalence ratio, 23

24 3.4 Flame propagation S u Measurements for the same mixture by different groups (a) 0 /S u, PREMIX S u % DE E + + B X X X X AF F F A A A A 26.4% D AE X B B + + B E A D E A + Taylor 1991 Aung et al Hassan et al Gu et al X BF + DE B DE B X A B D E F Rozenchan et al Qin and Ju 2005 Halter et al Hu et al % F F D D D B X D F + B E E X Tahtouh et al Halter et al Lowry et al Varea et al (linear) Varea et al (nonlinear) Beeckmann et al CH 4 /air at NTP Normalized by prediction of GRI Mech 3.0 Z. Chen (2015) CNF Very large discrepancy at very lean or rich condition Useless for restraining the uncertainty of chemistry 24

25 Collaborative work after the 1 st (2012) Workshop on Laminar Burning Velocity 25

26 3.4 Flame propagation S u Possible causes for the uncertainties in S u measurement: S b (cm/s) large radius low stretch affected by confinement, instability, radiation R fu H 2 /air, =4.5 T u =298K, P=1atm quasi-steady propagation R fl <R f <R fu R fl affected by ignition, unsteadiness K (1/s) small radius large stretch Mixture:, P, T u Ignition Buoyancy Instability Confinement Radiation Nonlinear stretch Extrapolation Z. Chen (2015) CNF 26

27 Confinement: P rise and compression Z. Chen, M.P. Burke, Y. Ju, Combust. Theory Modell. 13 (2009) Z. Chen, Combust. Flame 157 (2010) center r=0 flame front wall r=1 0.6 S u b b dr dt 0 f U b u b Flow velocity, U Spatial coordinate, r Flow effect: to induce inward flow and slow flame propagation Thermal effect: to increase T u and flame propagation speed 27

28 Radiation: thermal & flow effects Z. Chen, Combust. Flame 157 (2010) ( ) Adiabatic Radiative T u adiabatic 1900 T(K) 1800 ADI OTM S u b b dr dt 0 f u b T u radiative Thermal effect: to decrease the flame temperature & flame propagation speed Flow effect: to induce inward flow and slow flame propagation r(cm) ( ) 80 u(cm/s) ADI r(cm) r(cm) OTM r(cm)

29 Radiation: correction for fuel/air R H. Yu, W. Han, J. Santner, X. Gou, C.H. Sohn, Y. Ju, Z. Chen, Combust. Flame 161 (2014) Simulation results CH 4 C 3 H 8 ic 8 H 18 Fitting line R=0.82(S 0 u, ADI /S 0 )-1.14 Under-prediction due to radiation: R 1 S S 0 b, radiative 0 b, adiabatic R 0.82( S 0 u, ADI S 0 ) S 0 1cm/s S 0 u, ADI /S 0 Within 2% for S u0 >25 cm/s; within 5% for S u0 >12 cm/s Empirical correlation, R=R(S u0 ), for different fuel/air Radiation-corrected flame speed 29

30 3.4 Flame propagation instability Background: flame properties turbulent combustion Focus: Flame acceleration Jomassa & Law (2013) Channel flame 1.5 Tulip flame Ponizy et at. (2014) Y Review papers and groups: Kadowaki (2005) PECS Matalon (2009), Smooke (2013) PCI Matalon (2007), Candel (2014) Annual Rev. Fluid Bradley, Law, Ronney, Sun... Matalon, Oran, Bychkov, Liberman X Z. Chen (2014) 30

31 3.5 Flame & chemistry of fuel blends Background: Ignition control (RCCI) Alternative fuels (alcohol) Surrogate fuel model Focus: Ignition delay, flame speed Chemical mechanism Chemical interaction Transport/thermal effects Review papers and groups: Lu (2011), Reitz (2015) PECS Dooley (200) CNF Zuohua Huang, Xingcai Lü,... Ignition delay time [ms] Fuel blends: Gasoline + diesel Natural gas + H 2 Gasoline + ethanol PRF + toluene Syngas (H 2 +CO) 10 1 fuel/air mixture, φ = 1.0, p = 13.5 atm toluene iso-octane /T [1/K] n-heptane 31

32 3.6 Plasma assisted combustion Background: PAC: a new way to control combustion, emissions, and fuel reforming Mild Combustion Scramjet engine Plasma assisted combustion New engine technology Focus: Combustion control via PAC Plasma mechanism Plasma/combustion interaction PAC at high P / low T Neat experiments for modelling Review papers: Ju & Sun (2015), Starikovskiy (2013) PECS Starikovskiy (2015)???, Starikovskaia (2006) JPD-AP Starikovskii (2005) PCI Low Emissions Temperature increase Thermal O 2+,N 2 + Fuel Reforming Plasma discharge NO, O 3 O, H, OH N 2 *, N 2 (v) O 2 (a 1 Δ g ) Ions/electrons Radicals Int. species Excited species Kinetic Combustion Enhancement Ju & Sun (2015) PECS Cool Flames Ionic wind Instability Fuel fragments H 2, CO CH 4 CH 2 O Transport 32

33 3.6 Plasma assisted combustion S-curve (ignition & extinction) Flammability limits Sun et al. (2013) PCI Wolk et al. (2013) CNF 33

34 3.7 Meso-/microscale combustion Background: Micropower for MEMS High energy density Increased loss, friction Focus: Heat recirculation Surface reaction/quenching Flame quenching & stabilization Heat loss Radical loss Flame/wall interaction Thermal Chemical Catalytic combustion Liqud-gas mixing, fuel injection MIT micro-gas turbine (Epstein et al. 1997) wall Fuel/air U wall Heat recirculation heat S Convective or radiative losses radical Flame Review papers: Ju, Cadou, Matura (2015) Book Kaisare & Vlachos (2012) PECS Ju & Maruta (2011) PECS. Maruta (2011) PCI 34

35 3.8 other topics Supersonic combustion Microgravity combustion Mild combustion Cosmic combustion/supernova Catalytic combustion Multi-phase combustion Nano-particles, flame synthesis Detonation Fire From internet Gamezo et al. (2004) PRL 35

36 内容提要 1. 背景介绍 2. 代表性研究进展 3. 当前研究前沿 4. 总结展望 36

37 4. 总结与展望 理论分析 : 从 热 ( 单步反应 ) 到 反应 ( 多步反应 ); 从气相到多相 ( 喷雾 粉尘 表明催化 ); 从准定常到非定常 ; 从定性到定量 极端条件 ( 高压 超临界 近可燃极限 近稀释极限 富氧 高速 微重力等 ) 下的着火 火焰传播 失稳 熄火等基础燃烧过程及临界燃烧状态之间的转换机理 关键自由基的输运特性和关键基元化学反应对着火 火焰传播 熄火等基础燃烧过程的影响及控制作用, 冷焰与低温化学反应 37

38 4. 总结与展望 辐射与火焰的相互作用 火焰与流动的相互作用 火焰与壁面的相互作用 超临界条件下的基础燃烧特性 低温等离子体促进点火与强化燃烧的规律及机理 液雾动力学及其与化学反应 / 流动的耦合作用 催化燃烧 火焰合成 爆震敲缸 38

39 合作方向 : 球形传播火焰测量层流火焰速度 本课题组为该方面的实验提供基于详细化学反应机理的一维球形传播火焰模拟结果, 用于跟实验测量结果进行对比 已有合作单位和成果 Ju, Princeton [1] RWTH Aachen [2] CORIA-CNRS [2] ICARE-CNRS [3] IET-CAS [4] Syngas/Air 460K Su, m/s K Visualization sequence (tomography and Schlieren) of H 2 /air (E.R.=0.5, P= 0.1 MPa, T = 300 K) [2] Davis Mech (Davis et al. 2005) Sun Mech (Sun et al. 2007) K H 2 /CO/air, high P and T u [5] [1] F. Wu, W. Liang, Z. Chen, Y. Ju, C.K. Law, Proc. Combust. Inst. 35 (2015) [2] E. varea, J. Beeckmann, H. Pitsch, Z. Chen, B. Renou, Proc. Combust. Inst. 35 (2015) [3] L. Courty, K. Chetehouna, Z. Chen, et al., Combustion Science and Technology, 186 (2014) [4] M. Han, Y. Ai, Z. Chen, W. Kong, Fuel, 148 (2015)

40 谢谢大家! 感谢基金委的支持和齐飞老师 陈正北京大学工学院邮件 : cz@pku.edu.cn 发起并组织该会议! 网站 : 论文 : 欢迎大家过来交流 相互学习!